White/black is jarring, yeah. Light grey/dark grey is better most of the time. Other factors that affect readability I usually tweak are `max-width` and `font-size`, 35ems and at least 16px, respectively (except for microdata stuff which I usually keep between 12px-14px). In general, though, I prefer the content having visual focus, as opposed to the negative having focus (even though black text isn't usually described as the negative of the background).
